The boys' reacted just as Leaper expected they would, because, he said, "Boys are allowed to talk back to their parents more than girls are, to assert their will more."

Would girls react differently? I didn't think they would, but was I ever wrong.

Courteously, Morgan said, "It's good."

Again and again, the girls politely drank, even a girl who looked as if she was choking it down.

Only when I pushed them, did they tell the truth.

I asked one girl, Samantha, why she didn't tell me the lemonade tasted bad. She said, "I didn't want to be rude to you."

"I just didn't want to make anyone feel bad that they made this so sour," Asha told me.

Most boys didn't worry about that.

We tried another test, offering the kids brightly wrapped gifts. Again, following Leaper's advice, we filled each box with a disappointing gift: socks and a pencil.

Once again, the girls were polite.

Samantha said her gift was good. Another little girl, Courtney, was even more enthusiastic, saying, "Just what I needed. Socks and a pencil!"

I must say, the girls have a skill I lack; anyone who gives them a gift is going to feel good about it.

The boys weren't about to make me feel good. "What?" Raja said, "socks and a pencil? Rip-off!" Jacob had a similar reaction.

"This is one of those situations where the boys probably should be behaving more like the girls," said Susan Witt, who teaches childhood development at the University of Akron. She says boys and girls respond differently in situations like these because we parent them differently.

These differences came out when we asked the kids to describe themselves.

The girls described themselves as "nice," while the boys described themselves as "talented," "smart," "good at math," "funny." The boys rarely said "nice."

Both funny and nice are good. But often girls are too eager to be nice, says Witt, and boys too direct.

Is It Social or Biological?

So, can parents really change this? Maybe boys and girls are simply born different. "We're born differently," said Witt, "boys are XYs and girls are XXs. But, by and large, John it is primarily socialization and I believe that right down to my socks!"

By socialization, Witt means parents and society treat kids differently. And there is evidence of that. A famous study called "Baby X" designed by Phyllis Katz tested adults on how we treat babies based on what we think the sex is.

"We said this is Johnny. Just play with Johnny any way that you'd like. Or this is Jane. Just play with Jane anyway that you'd like," Katz said.

It was always the same baby. But when adults thought they were holding Jane, they held her gently, gave her dolls. When they thought the baby was Johnny, they offered him a football.

In the 1970s, some people took this to mean boys and girls were born entirely the same, and only behaved differently because sexist parents and a sexist society taught them to. Now, however, it's accepted that society and biology both create the difference.

Since parenting plays a part, maybe there's room for improvement.

Research in the workplace shows men's careers are hurt when men are too blunt, and some women achieve less because they're too nice.

When we tried our lemonade test on adults, the results were remarkably similar.

Georgetown Professor Deborah Tannen, who's written best sellers about gender differences, says each sex would benefit by adopting some of the opposite sex's traits. "For the men," Tannen said, "it might mean backing off, toning down or just saying a few words to show that you're cognizant of the other person's feelings," and women, she said, could work on being "more explicit in what they think and what they want and what they expect of the other person."

Reinforce Confident, Not Aggressive, Behavior

Can parents teach that? How could we teach the girls to be more assertive, and teach the boys to pick up on the girls' people skills?

Some families from our experiments let us put cameras in their homes, and we showed the tapes to Witt.

Witt offered a few tips for parents of girls: Don't help them so much. Research shows parents tend to help girls more than boys. This can make girls feel helpless and less confident. In addition, it's good to encourage girls to make choices.

In our tests, 9-year-old Patty didn't hesitate to tell us what she thought. And sure enough, our videotapes showed that in Patty's house, her parents prompt her to make choices about what to eat and drink, and what clothes she would like to wear.

"The girl who knows how to make a decision or starts making decisions when she's little," Witt said, "is going to be one of those girls who's better able to make decisions and assert herself as she gets older."

In the case of the boys who were maybe too honest in our test, we saw that their parents gave them a lot of freedom to act out. Maybe too much, says Witt.

For example, one boy shouted to his mother that he wanted something to drink. Moms should discourage kids who scream out demands, Witt said, perhaps by walking out of the room. Conversely, they should reward polite requests with a hug or kind words.

Finally, a caution about generalizing about gender. The differences between individuals are frequently bigger than differences between sexes. In our experiments, some girls did speak their mind, and some boys were very polite.